A study released today by the United States Geological Survey notes that the decline in snowpack in the Rocky Mountains since the 1980s is unusual compared to the historical evidence gathered from the previous centuries.
Studies previously released by the USGS and other institutions have attributed the noticed decline in snowpack to unusual springtime warming, more precipitation falling as rain rather than snow, and an earlier snow melt.
Due to the fact that 60 to 80 percent of the annual water supply for more than 70 million people living in the western US comes directly from winter snowpack melting, the current warming and the decline in the snowpack – which are only projected to worsen over the rest of this century – are causing scientists to worry about the amount of water that will be available.
“This scientific work is critical to understanding how climate change is affecting western water supplies,” Secretary of the Interior Ken Salazar said. “It helps land managers adapt to changing conditions on the ground, assists water managers with planning for the future, and gives all of us a better understanding of the real impacts that carbon pollution is having on our resources and our way of life.”
Partnering with the Universities of Arizona, Washington, Wyoming, and Western Ontario, the USGS led a study evaluating the recent declines in the snowpack by investigating 66 tree-ring chronologies which looked back 500 to more than 1,000 years.
Throughout that time, with a few exceptions in the mid-14th and early 15th centuries, the snowpack reconstructions showed that the northern Rocky Mountains experience large snowpacks when the southern Rocky Mountains experience smaller ones, and vice versa.
However, since the 1980s there have been simultaneous declines along the entire length of the Rocky Mountains, with unusually dramatic declines in the north.
“Over most of the 20th century, and especially since the 1980s, the northern Rockies have borne the brunt of the snowpack losses,” said USGS scientist Gregory Pederson, the lead author of the study. “Most of the land and snow in the northern Rockies sits at lower and warmer elevations than the southern Rockies, making the snowpack more sensitive to seemingly small increases in temperature. Also, winter storm tracks were displaced to the south in the early 20th century and post-1980s. Forest fires were larger, more frequent and harder to fight, while Glacier National Park lost 125 of its 150 glaciers.”
“The difference in snowpack along the north and south changed in the 1980s, as the unprecedented warming in the springtime began to overwhelm the precipitation effect, causing snowpack to decline simultaneously in the north and south,” explains USGS scientist and co-author Julio Betancourt. “Throughout the West, springtime tends to be warmer during El Niño than La Niña years, but the warming prior to the 1980s was usually not enough to offset the strong influence of precipitation on snowpack.”
While this year’s La Niña episode saw lots of snow in the north while there was severe drought in the south, the total amount of snow that fell was nothing in comparison to the century-long snowpack decline.